This invention relates to radars and other systems employing electronic signal processing and in particular to means for determining signal amplitude from the inphase and quadrature signal components utilized in such systems.
An amplitude detection is usually required in the radar and sonar signal processing to recover the signal amplitude from its inphase (I) and quadrature (Q) components. Theoretically, the signal amplitude may be obtained by forming the square root of the sum of the squares of the I & Q components. To circumvent the square root operation which demands an extraordinary amount of processing hardware, the amplitude is conventionally approximated by a linear detector. In a linear amplitude detector, the magnitude of the I and Q components are first compared to determine which one is larger. The larger magnitude is then summed with a fraction of the smaller magnitude to obtain an estimate of the signal amplitude. This approach is described in detail by G. H. Robertson, A Fast Amplitude Approximation for Quadrature Pairs, Bell System Technical Journal Vol. 50, pp 2849-2853, October, 1971 and by Morio Onoe, Fast Amplitude Approximation Yielding Either Exact Mean or Minimum Deviation for Quadrature Pairs, proceedings of the IEEE, July 1972. A fraction value of 0.5 is used in the Robertson Technique and other fraction values have been considered by Onoe.
Despite its simplicity in implementation, however, the linear detectors are beset with large estimation errors. For instance, the Robertson approach yields an error of 8.7 percent in the estimation of mean and a maximum deviation of 11.8 percent.
Accordingly there currently exists the need for an amplitude detector that can be implemented with substantial savings in digital processing hardware over square root operations and that also provides improved error performance over linear detectors. The present invention is directed toward satisfying that need.